Nanostructures formed from semiconducting materials are becoming more prevalent. Many different fabrication methods can be used to produce nanostructures, but they generally have not been able to offer complete control over the pattern and quality of the nanostructures in an affordable and timely manner. One of the most popular methods is reactive ion etching of a patterned substrate. However, this can result in intense damage to the crystal structure and surface morphology. Since many semiconducting applications are very sensitive to defects within the material, it is important to reduce them whenever possible. One method which is becoming increasingly used is metal-assisted chemical etching (MacEtch).
Metal-assisted chemical etching offers a method of etching silicon by patterning a silicon surface with a layer of metal. The metal acts as a catalyst for etching the silicon surface directly beneath it when exposed to an oxidizing agent (e.g., H2O2) and an acid (e.g., HF). Metal assisted chemical etching can produce vertical nanowires of high aspect ratios in silicon (e.g., see U.S. Patent Application Publication 2011/0263119, entitled “Method of Forming Nanoscale Three-Dimensional Patterns in a Porous Material,” which is hereby incorporated by reference in its entirety). Since it is a wet etch technique, MacEtch can be carried out economically in large quantities in comparison with popular dry etch methods, which may require a vacuum or plasma.